Manufacturing method of magnetic focusing equipment



March 19, 1963 susuMu YASUDA 3,081,527

MANUFACTURING METHOD OF MAGNETIC FOCUSING EQUIPMENT Filed Jan. 13, 1960 inventor S.YASUDA agent United States Patent Office 3,081,527 Patented Mar. 19, 1963 The present invention relates to a method of manufacturing magnetic focusing equipment for focusing an electron beam of a travelling wave tube or the like over a desired transit region. Although a uniform magnetic field is used for focusing the magnetic field of a long transit section, the so-called periodic magnetic field which varies with distance periodically on the axis may also be adopted.

The drawing illustrates an example of the package type electron tube for illustrating the manufacturing method of magnetic focusing equipment in accordance with this invention.

It has been publicly known that this type of system is extremely adaptable for manufacturing package type tubes in which the electron tube 1 and the focusing system 2 are fixed in position as an entirety as shown in the drawing. In this way the magnetic circuit can be made very compact. This type of magnetic circuit consists of cylindrical permanent magnets 3 and ring pole pieces 4 combined with the permanent magnets as shown in the drawing. in this case, each of the cylindrical permanent magnets has a small ratio of length to diameter and they are subject to a strong counter magnetic field with each other because they are so arranged in assembling that the magnetic poles of the same polarity face each other.

Moreover, demagnetisation of the magnets occurs due to handling; which results in the utilization of magnets having a large coercive force such as barium ferrite magnet. The defect of this type of magnet is that it is susceptible to temperature change. Some of the effects that a magnet receives by temperature change are reversible while others are irreversible. When magnets using a material having a large irreversible change are magnetized and used in package type tubes in frigid localities there arises a problem that the current transmission is extremely lowered due to the corresponding changes in the focusing ability of the magnet. Therefore, use of equipment in such localities becomes impossible on account of the irreversible change of the magnets caused by the temperature change such tubes receive when subjected to frigid temperatures.

The following facts were determined by the inventor in accordance with a performed experiment.

Two sets of barium ferrite focusing magnets that produce a periodic magnetic field of a maximum of 850 gauss and 1380 gauss respectively, were magnetized at room temperature in a field having a coercive force of about 1900 oersteds and a residual magnetism of about 2400 gauss. The magnets were then cooled at -50 C. and then restored to room temperature. As a result of remeasurement a lowering in intensity of the magnetic field of 6% and 8% was produced for the former and latter, respectively. The effect due to heating was not admitted even if measurement was made at room temperature after cooling at -50 C. and then heating to +70 C.

This experiment shows that the irreversible change of magnetic properties of barium ferrite magnet can be made negligible in the conceivable temperature range provided the magnet has had a cooling history at the lowest intended temperature range to which the magnets are subjected after they are magnetized.

Moreover, the degree of lowering in magnetic field intensity is dependent upon the operating point of the magnet on its demagnetizing characteristic curve, or stated otherwise, the larger the field intensity the more irreversi ble effect can be expected.

The present invention is characterized by producing sufficient low-temperature cooling history to permanent magnets prior to use in manufacturing electron-tube focusing equipment using permanent magnets.

In manufacturing equipment of this kind the ferrite pieces are arranged with suitable pole pieces and then magnetized. The magnets and pole pieces are then assembled in approximately the same positions as under normal operating conditions. The focusing assembly is then cooled to the lowest intended temperature and thereafter finally assembled with the remaining travelling wave tube equipment. The ferrite pieces may, in the alternative, be first magnetized and thereafter cooled to the lowest intended temperature. In either case, cooling is effected after magnetization of the ferrite pieces. By so doing, the characteristics of the ferrite magnets do not irreversibly change even though the temperature of the magnets may subsequently be raised to normal or relatively high operating temperatures or even if cooled to a low temperature which is not lower than the predetermined lowest temperature.

The lowest temperature should preferably be as high as possible, because cooling the magnet at too low a temperature results in too much deterioration of the magnetic properties resulting in a decrease of the focusing field. Thus, if the operating temperature of the magnet at the destination would not be lower than 10 C., for example, cooling temperature of 10 C. is necessary and suflicient. If the destination temperature would be -69 C. (which would be encountered during transportation of a product by an airplane through the height of 40,000 feet), the magnets should be cooled during the manufacture of the product to 69 C. For Antarctic use of the product, cooling to about l00 C. would be necessary. Cooling temperature, therefore, cannot be restricted to certain values but depends solely upon the temperature of the ultimate destination to which the travelling wave tube is to be shipped.

Then, so far as the irreversible change of focusing action of the equipment is concerned, the high quality of the package-type tube previously cited can be maintained without impairing the optimum focusing capability that the tube gained by precise adjustment in the course of manufacturing even if it is placed under low temperatures during transportation to frigid localities or high ambient temperature at tropical region.

It will be understood that although the present invention has been described above with reference to a package type tube, this invention is by no means restricted to the package type, but may equally be applicable to magnetic focusing equipment in general using materials having comparatively large irreversible change. This latter case is also comprised within the scope of the present invention.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. The method of treating permanent magnet material subject to irreversible magnetic characteristic changes at low temperatures comprising the steps of magnetizing said material, and then cooling said material to the lowest ambient temperature below room temperature expected in use, storage and transportation; whereby reversible magnetic ch racteristics in the expected temperature range are secured.

2. The method of treating permanent magnet material of ferrite composition to secure reversible magnetic characteristics at temperatures below 10 C. comprising the steps of magnetizing said material, and then cooling said material to the lowest ambient temperature below -10 C. expected in use, storage and transportation.

3. The method of treating permanent magnet material of barium ferrite composition to secure reversible magnetic characteristics at temperatures below 10 C. comprising the steps of magnetizing said material, and then cooling said material to the lowest ambient temperature below -l0 C. expected in use, storage and transportation.

5 References Cited in the file of this patent UNITED STATES PATENTS Rathenau Mar. 18, 1958 OTHER REFERENCES Calhoun: Supplement to J. of Applied Physics, vol. 30, pages 2935 and 294$, April 1959. 

3. THE METHOD OF TREATING PERMANENT MAGNET MATERIAL OF BARIUM FERRITE COMPOSITION TO SECURE REVERSIBLE MAGNETIC CHARACTERISTICS AT TEMPERATURES BELOW -10* C. COMPRISING THE STEPS OF MAGNETIZING SAID MATERIAL, AND THEN COOLING SSAID MATERIAL TO THE LOWEST AMBIENT TEMPERATURE BELOW -10* C. EXPECTED IN USE, STORAGE AND TRANSPORTATION. 